Many processes result in the production of a solution or suspension that contains undesirable constituents or contaminants. It may be desirable to remove a proportion or all of the contaminants in the solution or suspension, to reuse the resultant solution in the same process, to use the resultant solution and/or the contaminants in another process and/or to dispose of them in an appropriate manner. For example, in the textile industry it is advantageous to remove dyes from solutions or suspensions to minimise the environmental impact when disposing of the solution. It may also be desirable to remove contaminants from a solution or suspension in certain sweetener industries, where very salty and highly coloured solutions are also present.
Specifically during sugar refining, it is necessary to remove non-sugar components from the raw sugar. Such non-sugar components include colorants or colour bodies, which are present in the raw sugar when it is extracted from the plant, and further colour bodies that are produced during processing. Other components that may be present in the raw sugar solutions include impurities and fouling agents. The non-sugar components include high molecular weight compounds, such as colloids, waxes and phenolic compounds.
Ion exchange resins can be used to remove the colour bodies, impurities and fouling agents from the sugar solutions. This process is commonly known as decolourisation.
Following the use of ion exchange resins for the decolourisation of sugar solutions, the colour bodies, impurities and other fouling agents may be removed from the resin, to regenerate the ion exchange resin so that it can be used again in decolourisation reactions. A salt solution can be used for the regeneration of ion exchange resins, and the resulting ion exchange regenerant material may have high concentrations of salt and contaminants including colour bodies and non-coloured components.
The ion exchange regenerant material may be disposed of by general waste water disposal, such as by treatment at a sewer plant or an alternative waste water treatment plant. The disposal of the ion exchange regenerant material in this way can present a severe pollution problem. It is therefore of both economic and environmental benefit to reuse as much of the ion exchange regenerant material as possible.
The use of membrane filtration to remove contaminants from waste streams, such as ion exchange regenerant material, is known. However, the ability of membrane filtration to remove the contaminants is dependent on a number of factors, such as pH and temperature. In particular, the concentration of the contaminants in the waste stream can affect the efficiency of the membrane filtration. If the concentration of contaminants is too high, membrane filtration may be inefficient and the membranes may become damaged. Therefore, the use of membrane filtration to remove contaminants is limited to waste streams with sufficiently low levels of contaminants. In the case of removing contaminants from ion exchange regenerant material, this can result in only a fraction of the ion exchange regenerant material undergoing membrane filtration so that it is suitable for reuse, and the remaining ion exchange regenerant material must be disposed of, which may be costly and/or wasteful.
However, a process to remove the contaminants from a solution or suspension in addition to or in place of membrane filtration would allow a larger proportion of the waste material to be reused and considerably reduce the amount of waste material produced.